Sand filter apparatus for swimming pools



Dec. 5, 1961 A. c.'MccoY 3,011,643

SAND FILTER APPARATUS FOR SWIMMING FOOLS BYZ Dec. 5, 1961 A. c. MocoYSAND FILTER APPARATUS FOR SWIMMING PooLs Filed March 25, 1959 2Sheets-Sheet 2 IN V EN TOR. HW/v (i ,/Vffof/ United States Patent O3,011,643 SAND FILTER APPAATUS FOR SWIMlVIlNG P OLS This inventionrelates to a sand filter apparatus and system for use in fil-tering thewater for swimming pools and the like.

Conventional sand-bed filters, comprising numerous graded layers ofloose sand and rock, provide an excellent filtering -action and arereadily cleaned of contaminants by merely backwashing or backtiushingwater upwardly through the beds. Such backwashing provides ahighly-effective cleaning action since the iiner filter material at theupper portion of each bed is lifted into the water where each particlemay be cleaned on all sides. However, such beds are excessively bulkyand expensive, particularly where the system is to be employed inconnection with a family-size `swimming pool or other relatively smallequipment.

Because of the great bulk and expense of conventional sand-bed filters,it has become common practice to employ lters in which the swimming poolWater is merely passed through a strainer or a bag of filter material.After the pores in the strainer become clogged With contaminants, it ispartially cleaned or else thrown away, it being impractical orimpossible to effect thorough cleaning. Such filter apparatus,furthermore, does not provide an effective ltering action.

It has also been proposed to provide cakes of iilter material in whichsand was bonded together in a suitable manner. Such cakes comprised theactual filtering medium, and were unsatisfactory since the bonded sandwas not readily or satisfactorily cleaned of contaminants. One suggestedsolution to the problem of cleaning lter cakes was to break up thecakes, clean the sand and then re-combine the sand into cake formthrough use of a suitable adhesive. Such-a suggested .solution was,however, impractical and excessively expensive.

In view of the above factors characteristic of filter apparatus, it isan object of the present invention to provide an improved sand filterapparatus which is small and compact in size and economical tomanufacture and use, yet which produces a highly-effective filtrationoperation.

A further object is to provide a small land compact sand filterapparatus in which loose particles areemployed as the filtering medium,so that backwashing will effect a thorough and efiicient cleaning ofcontaminants from the lter.

A futher object of the invention is to provide a combination filter baseand underdrain header adapted to provide a uniform fiow of water duringthe baekwash cycle, and constructed as a rigid unit whereby theunderdrain header may have lminimum strength for economy of production.

A further object is to provide overdrain and underdrain constructionsadapted to provide uniform flow of water mrough the filter apparatus, tothereby minimize v channeling and eruption effects and reduce therequired freeboard distance to a minimum.

A further object is to provide a filter apparatus incorporating novelmeans for preventing channeling of water down the sides of the sand bed,so that the water must pass through the sand itself.

A further object is to provide a plurality of small and compact filterunits which may be used either singly or in multiple, in combinationwith conduit means adapted to effect selective fiow of water to thefilter units during 3,011,543 Patented Dec. 5, 1961 backwashing so thata relatively small-capacity pump may be employed and still provideefficient cleaning of contaminants from each unit.

These and other objects and advantages of the invention will be setforth more fully in the following specification and claims, consideredin connection with the attached drawings to which they relate.

In the drawings:

FIGURE 1 is a vertical central sectional view illustrating a two-unitfilter apparatus constructed in accordance with the present invention,in combination with conduit and valve means for connecting the units inpmallel during the filter cycle and'independently during the backwashcycle;

FIGURE 2 is a plan view of the showing of FIG- URE 1;

FIGURE 3 is a horizontal section taken on line 3 3 of FIGURE 1, andlooking in an upward direction as indicated by the arrows;

FIGURE 3a is a perspective view of one of the unitary filter lbase andunderdrain header assemblies, portions being ibroken away to illustratethe underdrain laterals independently of the surrounding rock medium;

FIGURE 4 is an enlarged fragmentary perspective view illustrating themeans for preventing channeling of water down the sides of the filtersand bed;

FIGURE 5 is a vertical section showing an anti-Siphon valve connected inthe conduit means; and

FIGURE 6 is an enlarged fragmentary section of a portion of the baseunit.

The apparatus of the invention may comprise one or any number ofindependent filter units which may be small and compact, and which maybe mounted in either stacked or laterally-spaced relationship. Two suchunits are shown in FIGURE l and are numbered 1t? and 11. Except as maybe specifically stated hereinafter, the units Vmay be substantiallyidentical. Accordingly, only one unit Will be described in detail.

Each unit comprises a generally tubular metal wall 13 in one end ofwhich is welded what may be termed the bottom member 14, although it isto be understood that such member also serves as the cover for the nextlower unit. At the upper end of wall 13 is welded an annular seat member15 having a channel-shaped cross section and containing a sealing meansor substance 16. Seat member `15 is adapted to seat either theperipheral portions of wall 1-3 and the connected bottom member 14, asshown generally at the center of FIGURE l, or else to seat theperipheral portion of atop cover '17 as shown at the upper part ofFIGURE l. Suitable swing-bolt connectors 18 are provided to maintain theelements in tightly-assembled relationship whereby adequate seals areprovided at 16. The bottom members 14 and top cover 17 are lpreferablydome-shaped to facilitate removal of air from the system.

Itis an important feature of the invention that the base or support forthe loose filter sand comprises a rigidly-cast unit 21 (FIGURE 3a)incorporating bonded stones or gravel in which is embedded theunderdrain header 22. Stated more specifically, :the base unit maycomprise a number of inches of relatively small-diameter gravel orstones, for example 1A. inch in diameter, and indicated at 23 in`FIGURES. 3a and 6. A thinner layer of smallerdiameter stones, forexample 1A; inch in diameter, is cast over the layer 23 and is indicatedat 24 in FIGURE 3a. The stones in layers 23 and 24 `are all bondedtogether, to form a disc, by coating each stone with a suitable adhesivesubstance 25 (FIGURE 6) and then casting the coated stones in the bottomof tubular element 13 over bottom member 1,4. It has been found that athermosetting synthetic bonding resin, such as of the polyester or epoxytypes, is highly satisfactory for this purpose. Such resins,

which make use of suitable catalysts, are well known in the ar-t of boatbuilding, for example. It is emphasized that .the resin does not fillthe voids between the individual stones, but instead coats each stone inorder to effect rigid bonding between all of the stones whilemaintaining the voids therebetween.

Underdrain header 22 comprises a relatively largediameter tubularplastic pipe or manifold 26 from which a substantial number ofsmaller-diameter laterais 27 are projected to provide relatively uniforminflow of water into the coarser layer 23 of the base unit. Each lateralhas a substantial number of outlet openings therein, indicated as thearcuate slots 2S which are provided in the undersides only of thelaterals. In order to provide inflow of water to the laterals 27 atrelatively uniform pressures and velocities, a plurality of baffles 29and 30 are provided in pipe 26 as illustrated in FIGURE 1. Thus, thebaffle 29 at the portion of the pipe relatively near the inlet endthereof is shown as being relatively small, occupying somewhat less thanhalf the cross-sectional area of the pipe. Batlle 3G, relativelyadjacent the closed end 31 of pipe 26, is larger in area and occupiesmore than half of the cross-sectional area of the pipe. If it were notfor the presence of the baflies 29 and 30, a much larger amount of waterwould flow through the laterals adjacent the closed end 31 than adjacentthe inlet end of the pipe. It is pointed out that the plastic pipe 26and laterals 27 may be relatively thin-walled and economical inconstruction, this being because they are supported by the rigidly-castrock 23 in which they are embedded.

An overdrain header 32 is mounted horizontally -in each unit and inspaced parallel relationship above the underdrain header 22 therein.Header 32 compris a tubular plastic pipe having suthciently largediameter to be selfsupporting, so that it may be cantilevered from oneportion of Wall 13. The header pipe 32 has a plurality of arcuateopenings 33 and 34 provided in spaced relationship therein and on onlythe upper side thereof. Thus, opening 33 is adjacent the closed end 36of the header pipe, whereas'cpening 34 is intermediate the opening 33and the inlet end of the pipe. A baffle 37 is mounted in the pipe 32adjacent opening 33 in order to equalize' the rate of flow of waterthrough the openings 33 and 34. Such baiile extends completely'acrossthe header 32 in a di'- rection perpendicular to the plane of drawingFIGURE l. Disposed in a portion of the space between overdrain header 32and the upper surface of base unit 21 is a bed 38 of loose filter sand.The sand in that portion of bed 38 which rests on the base unit 21 has adiameter suiciently large to prevent sifting into the intersticesbetween the stones which comprise layer 24, whereas the upper portion ofbed 38 is extremely fine to provide the mosty effective filter action.For example, a major portion of the bed, and the one which rests on base21, may comprise No. 16 sand. A relatively thin layer of No. 20 sand maybe disposed on the upper surface of the No. 16 sand. Potassium alum orother suitable and conventional filter substance may be employed ifdesired. The numbers given represent U.S. Standard sieve sizes.Referring to the showing of unit in FIGURE 1, the vertical dimensionbetween the upper surface of the sand bed and the openings 33 and 34 isdesignated A and is known as the freeboard, distance. The-verticaldimension between such openings and the cover 17 is designated B, and isknown as the cushion distance.

The freeboard distance A is made just great enough that no filter sandwill be discharged out through overdrain header openings 33 and 34during backwashing of water'upwardly from underdrain header 22 tooverdrain header 32 for the purpose of cleaning the filter bed ofcontaminants. The cushion distance, designated B, is made just greatenough to effect uniform water ow and pressure in the upper end of eachunit 10, etc., so that thewater which ows downwardly from such upper endduring the filter cycle will have a relatively uniform pressure and owdistribution throughout the entire surface of the filter bed. Thesedimensions vary somewhat in accordance with the factors including thewater pressure, particle size of the sand, etc. They are, however,particularly in the case of freeboard distance A, much smaller than inconventional filter beds because of the uniform water pressure and flowdistribution effected by the base unit 21, baille means 29 and 30, etc.

Means are provided to prevent channeling or sidewashing of water downthe sides of Vthe filterV bed 38, instead of through the bed as isdesired. As best shown in FIGURE 4, such means comprises a roughanti-channelting coating 39 formed on the entire inner surface oftubular wall 13 around the filter bed 38, and an annular rib or flange40 which projects inwardly from surface 39 and is continuous throughoutthe entire circumference of the wall 13. Preferably, the coating 39 andrib 40 are integrally formed of No. 12 or No. 16 sand which is bondedtogether, and to wall 13, by means of a suitable adhesive such as theone employed to cast the stone layers 23 and 24. It is pointed out thatthe sand in sand bed 38 is disposed on both sides of rib 40, making itnecessary that water actually pass downwardly through the sand bedinstead of merely around the edges thereof.

Proceeding next to a description of the conduit, valve and pumrp meansassociated with the filter units, these comprise (FIGURES 1 and 2) afirst pipe 41 connected to both of the underdrain headers 22. Pipe 41extends upwardly :to a point above cover 17, so that water may not drainfrom the filters when the pump is not operating. Pipe 41 connects to asuitable shut-off valve 42 which in turn connects to an anti-Siphonvalve 43 and thence through a pipe 44 to the swimming pool. Theoverdrain headers 32 connect through shut-off valves 46 and 47 to a pipe48 the lower end of which connects through a valve 49 to a waste drain.The upper end of pipe 48 connects through a shut-off valve 511 to across or T connector 52. Connector 52, in tin-n, connects to a pipe 53and pump S4 and thence to the swimming pool, and also connects through avalve 56 to the previously-described pipe 41 from the underdrain headers22.

A suitable anti-Siphon valve 43 is indicated in FIGURE 5 as comprising afloat 57 adapted, when the valve is full of water, to engage a seat 53and prevent outflow of Water from the valve. However, when there is nowater in the valve the float drops and permits inflow of air throughports 59, so that no siphoning action may occur. This insures that thefilter units will always remain full of water, as is necessary in orderto prevent formation of holes or channels in the filter bed when theequipment is again put in operation.

Means are provided to remove trapped air from the filter units, andcomprise air lines 61 and 62 connected, respectively, to the center ofcover 17 and to the center of the bottom 14 of unit 10. The latter airline, number 62, extends through the cast base layer 23. The air linesextend to the pipe 44 leading to the pool, but may be tapped by openinga valve 63 which leads to waste. Thus, air may be tapped by merelyopening the valve 63 and leaving it open until all air is exhausted.When the valve 63 is closed, a very small amount of water may ow throughthe lines 61 and 62 to the pool.

It is emphasized that the diameter of the stones in layer 24 should beas large aspossible while still providing support for the loose sandbed. Also, the diameter of the stones in layer 23 should besubstantially larger than in layer 24. The result is that the voids inlayers 23 and 24 are so large that they will not become clogged with theminerals present in the Water. The voids are also su'- ciently large topermit rapid and effective flow of water during backflushing. If thebase were formed of bonded sand instead of the stones, neither of theseimportant benefits would result. If the stones were not bonded together,they would be irregularly moved about by the b rapidly-flowing waterduring back-flushing and would not perform their function of uniformlydistributing the ow.

Operation Each lter unit may be economically manufactured by merelymounting the underdrain header 22 imposition and then casting the layer23 therearound after the individual stones have been coated with theadhesive 25. The layer 24 is then cast over layer 23, following whichthe antichanneling coating 39 and rib or flange 40 are adhesivelyapplied as described above. The overdrain header may be readily mountedin cantilevered relationship, and the loose sand layer 38 may beintroduced at any stage in the operation subsequent to the setting ofthe adhesive.

The required number of lter units lil-11, etc., may then be readilymounted at the desired locations, and in either stacked or lateralrelationship. Let it be assumed that the units are mounted and connectedas shown in FlGURES l and 2, and are associated with a conventionalswimming pool.

During the filter cycle, the valves 49 and 56 are closed, and valves 42,46, 47 and 51 are open. Pump 54 is then run in a direction effectingupow of water through pipe 53 and thence into the overdrain header 32 ofeach unit. Such water flows out the openings 33 and 34 in the overdrainheader at a substantially equal rate, and flows upwardly into thecushion region indicated at B in FIGURE l. The water pressure and iiowin cushion region B becomes uniformly distributed throughout thediameter of the unit, following which the water flows downwardly throughthe loose sand bed 38, bonded layer 24, bonded layer 23, openings 28 inthe underdrain header laterals, pipe 26, pipe 41 and pipe 44 back to theswimming pool. The anti-channel means 39 and 40 prevent channeling ofwater down the sides of the sand bed. A very excellent filter action isthus effected in the loose sand bed 38 of each unit, which finallyresults in the depositon of much contaminants therein.

In order to effect a backwashing or backflushing of the water to therebyclean the units of contaminants, valves 42 and 51 are closed, and valves49 and 56 are opened. Pump 54 is then operated to effect flow of waterthrough pipe 53, crossover 52, and pipe 41 to the underdrain header 22of each unit. The water then flows out through the underdrain laterale27 and the cast rock, and up through the sand bed 38 to the overdrainheader 32, from whence it flows outwardly through a pipe 48 to waste.The upward flow of water through the loose sand bed causes the entirebed to be lifted or boiled into the water, so that the contaminants arethoroughly cleaned from the individual filter material particles. Aspreviously stated, however, the freeboard distance A is made sufficientthat no sand will flow outwardly through the openings 33 and 34 and thusbe Wasted.

It is emphasized that the combination of the baies 29 and 36, thelaterals 27 and the cast rock layers 23 and 24 cause the flow of waterto be very well and equally distributed throughout the filter units.Furthermore, the water initially flows downwardly from the underdrainheaders 22 and then upwardly therepast, so that there is very thoroughflow and pressure distribution. The upwardly-flowing water musttherefore pass through the boiling filter sand 3S in a highly uniformmanner which prevents points of eruption. Because of the absence of sucheruption, etc., the freeboard distance A may be made very small, asstated, without danger that filter material will be wasted. During thefilter cycle, the uniform water pressure and flow prevent the filtermaterial from being pitted or gullied, so that filtering is uniform andeffective.

Itis a feature of the invention that the pump 54 may be relatively smallin capacity while still providing a thorough back-flushing action. Thisis made possible because the ow of water during the filter cycle may berelatively small, such as 3 to 5 gallons per minute, in comparison tothe flow of water for backflushing, such as l0 to l2 gallons per minute.Such a volume of flow during backushing is achieved by alternatelyclosing the valves 46 and 47, so that each unit 10 and 11 is separatelybackflushed with the relatively small-capacity pump 54. In summary, thepump S4 which is adequate to handle both units during the filter cycle,when water ow is small, is also adequate to handle each separate unitduring backwashing when the water flow for each unit is greater.

After completion of -backushing the valves are returned to their initialpositions so that the filter cycle may be resumed. The boiling sand thensettles down onto the base, in stratified layers.

It is strongly emphasized that the cast base unit k21 (FIGURE 3a) notonly provides a highly efficient distribution of fiow duringbackiiushing, but also enormously reduces the height of the supportingmedia upon which the loose sand 38 rests. Thus, in conventional sandfilters there would be numerous rock layers, of progressively increasedrock sizes, below the layer 23 illustrated herein. The resulting greatreduction in the height of the base for the loose sand, and theextremely uniform distribution of water pressure and flow, mean that theheight of each filter unit may be less than half that of a conventionalsand filter having the same capacity. kSuch a size reduction, with theattendant reduction in cost and space required, make it practical toemploy the present filter in conjunction with small swimming pools, sothat the owners of such pools may have the benefits of improved cleaningand filtration.

To summarize and amplify upon the above description of the advantages ofthe cast base 21, certain of the undesirable results which would occurif the stones in the base were not bonded together will now bementioned: (a) During the backiiush cycle, the stones would rise, shiftand become disuniforrn, thereby encouraging channeling, eruptions andother undesired results. (b) The bed or base would not produce abalanced rate of water flow per square foot, that is to say would notbreak up the water flow as described above. (c) The lighter stones inthe bed or base would be enabled to iiow up into the sand, duringbackliushing, and would be replaced by sand so that flow of sand to thepool could result. (d) The strength and rigidity of the underdrainheader 22 would need to be increased. (e) A much greater depth of rockwould be required. (f) The bonded base 21 is immune to the bomb-likeedects of air mixed with the backflush water, and minimizes thepossibility that balls of dirt may form in the filter.

It is to be understood that the terms stones, rock etc., include notonly actual stones and rocks but also synthetic stones or rocks such asmay be formed of plastic, for example. The same applies to sand, itbeing understood that natural sand may be replaced by certain types ofsynthetic materials.

Various embodiments of the present invention, in addition to what hasbeen illustrated and described in detail, may be employed withoutdeparting from the scope of the accompanying claims.

I claim:

l. A small and compact swimming pool filter including in combination:side, cover and bottom walls detining a closed filter chamber; anoverdrain header in the upper portion of said chamber and means forselectively supplying thereto during the filter cycle the pool Water tobe filtered and for withdrawing therefrom during the` backwash cycle thebackwash Water; an underdrain header extending in a shallow lower zoneof said chamber and providing a plurality of orifices distributeduniformly throughout the horizontal cross section of said chamber andmeans for selectively supplying thereto the backwash water during thebackwash cycle and withdrawing therefrom during the filter cycle thefiltered pool water; a rigid cast mass of adhesively coated relativelysmallV diameter stones substantially filling said shallow lower zonearound said underdrain header in enclosing and supporting relationshiptherewith, the minimum diameter 0f said stones being of the order ofabout one-eighth inch and the maximum diameter of said stones being ofthe order of about one-fourth inch, the adhesive coating of said stonescomprising a synthetic bonding resin selected from the class consistingof polyester resins and epoxy resins, said adhesive coating being usedin amount suiiicient only to surface coat said stones and bond same intosaid rigid mass while maintaining therebetween Yvoids; and a mass ofloose lter sand in said chamber having a Vlower stratum supported onsaid rigid mass of stones composed of particles larger than said voidsbetween said coated stones and an uppermost stratum of iiner sandterminating in an upper surface spaced below said overdrain header.

2. A swimming pool filter as deiined in claim 1 in which said suppersurface is spaced only a small freeboard distance below said overdrainheader, said distance being less than the depth of said mass of looseiilter sand.

3. A swimming pool lter as dened in claim 1 in which said rigid mass ofadhered stones comprises a lower stratum of stones having a diameter ofthe order of onefourth inch and an upper stratum of stones having adiameter of the order of one-eighth inch, the stones of each stratumbeing bonded together and to the stones of the other stratum byk saidsynthetic bonding resin.

4. A swimming pool lter as dened in claim 3 in which said underdrainheader is positioned exclusively in said lower stratum of stones.

5. A swimming pool ilter as dened in claim 1 in which said overdrainheader includes at least one large pipe having upwardly facing openingsspaced below said cover wall a cushion distance slightly larger thansaid freeboard distance.

6. A swimming pool iilter as defined in claim 1 including a roughanti-channeling coating on the inner surface of said side wall aroundthe mass of loose iilter sand, and an annular rib projecting inward as aledge from said inner surface into said mass of loose lter sand at alevel below the top thereof.

7. A swimming pool ter as dened in claim 6 in which both said coatingand said annular rib comprise particles of sand bonded together by saidsynthetic bonding resin.

References Cited in the iile of this patent UNITED STATES PATENTS UNITEDSTATES PATENT OFFICE CERTIFICATION OF CORRECTION Patent No. 3Oll,643December 5V l96l Alvin McCoy It is hereby certified that error appearsin the above numbered patent requiring correction and that the saidLetters Patent should read as corrected below.

Column lY line 54 for "futher" read further column 3 line 63, for@"freeboard,"y read "freelooalr'd',x column 7g line l8g for "supper"read upper' Signed and sealed this 24th day of April 1962.

(SEAL) Attest:

ESTON GQ. JOHNSON DAVID L.- ,LADD Attesting Officer Commissioner ofPatents

